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MBB 231 > Lecture 15 - Cytoskeleton & CM: Microtubules > Flashcards

Lecture 15 - Cytoskeleton & CM: Microtubules Flashcards

1
Q

what are the 5 roles of the cytoskeleton?

A
  1. scaffolding that provides structural support
  2. network of tracks to direct the movement of material
  3. force generating apparatus for movement and contraction
  4. a framework for positioning various organelles within the cell
  5. essential component of the cell division machinery
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2
Q

__________ are the largest of the cytoskeletal components of the cell

A

microtubules

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3
Q

what are the 2 types of microtubules in the cell?

A
  1. cytoplasmic microtubules
  2. axonemal microtubules
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4
Q

what are cytoplasmic microtubules responsible for?

A
  • maintaining axons
  • formation of mitotic and meiotic spindles
  • placement and movement of vesicles
  • maintaining or altering cell shape
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5
Q

what are axonemal microtubules responsible for?

A
  • cilia
    -flagella
  • basal bodies to which cilia and flagella attach
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6
Q

def: the central shaft of a cilium or flagellum, is a highly ordered bundle of MT’s

A

axoneme

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7
Q

what are the protein building blocks of microtubules?

A

tubulin heterodimers

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8
Q

MT’s usually consist of 13 longitudinal arrays of polymers called ___________

A

protofilaments

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9
Q

what is the basic subunit of a protofilament?

A

heterodimer of tubulin, one alpha-tubulin and one beta-tubulin
bind covalently to form alpha-beta- heterodimer

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10
Q

T or F: all the dimers in the MT are oriented the same way

A

true

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11
Q

as a result of their dimer orientation, all protofilaments have _______ _________

A

inherent polarity

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12
Q

cytoplasmic MTs are _____ ______ with 13 protofilaments?

A

simple tubes

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13
Q

some axonemal MTs form _______ or ________ MTs

A

doublet or triplet

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14
Q

where can doublet MTs be found

A

in cilia and flagella

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15
Q

where can triplet MTs be found

A

in basal bodies and centrioles

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16
Q

when does reversible polymerization of tubulin dimers occur?

A

only in the presence of GTP and Mg2+

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17
Q

def: dimers aggregate into oligomers, which serve as “nuclei” from which new MTs grow

A

nucleation

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18
Q

def: the addition of more subunits at either end

A

elongation

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19
Q

how do the lag phase and elongation phase compare

A

the lag phase starts off slower since nucleation is a slow process but then the elongation phase is much faster

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20
Q

def: when the concentration of tubulin becomes limiting, the assembly is balanced by disassembly

A

plateau phase

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21
Q

def: concentration in which MT assembly is exactly balanced by disassembly

A

critical concentration

22
Q

where does the addition of tubulin occur quicker?

A

the plus ends of the microtubules

23
Q

T or F: the plus and minus ends of microtubules have the same critical concentation

A

false, they differ

24
Q

def: addition of subunits at the plus end, and removal from the minus end

A

treadmilling

25
Q

if [tubulin subunits] is above critical concentration for the plus end but below the minus end, _________ will occur

A

treadmilling

26
Q

when is the GTP bound to the submit hydrolyzed to GDP?

A

after the heterodimer is added to the MT

27
Q

is GTP hydrolysis required for MT assembly?

A

no, it is needed to promote interactions and addition to MTs

28
Q

def: one population of MTs grows by polymerization at the plus ends whereas another population shrinks by de-polymerization

A

dynamic instability model

29
Q

the GTP cap at the plus end prevents _________ __________

A

subunit removal

30
Q

growing MTs have _____ at the plus ends, and shrinking MTs have ______

A

GTP, GDP

31
Q

hydrolysis of GTP after assembly changes the conformation of the subunits and tends to force the protofilament into…….

A

a curved shape that is less able to pack into the microtubule wall

32
Q

which end of the microtubule has a higher critical concentration and therefore will grow slower?

A

the negative end, the plus end will grow faster at the same concentrations

33
Q

def: where MTs originate from, serves as a site of MT assembly nucleation and acts as an anchor for one end(minus)

A

microtubule-organizing centre (MTOC)

34
Q

an example of an MTOC in cells during interphase is

A

centrosome near the nucleus

35
Q

centriole walls are formed by ___ ____ ___ ________ and are oriented at ___ ____ to each other

A

9 sets of triplet microtubules, right angles

36
Q

can cells divide without centrioles?

A

yes, but they have poorly organized mitotic spindles

37
Q

where are gamma-tubulins found ?

A

only in centrosomes

38
Q

def: nucleate the assembly of new MTs away from the centrosome

A

gamma- tubulin ring complexes (gamma-TuRCs)

39
Q

what does loss of gamma-TuRCs prevent?

A

prevents the cell from nucleating MTs

40
Q

what is the most important role of MTOCs?

A

the ability to nucleate and anchor MTs

41
Q

which end of the MTs are anchored in the MTOC

A

the minus end

42
Q

what are the 4 ways that cells control microtubule assembly and structure?

A
  1. MT-binding proteins that use ATP to drive vesicle or organelle transport or generate sliding forces between MTs
  2. Microtubule-Stabilizing/Bundling Proteins
  3. Plus-End Tubulin Interacting Proteins
  4. Microtubule-Destabilizing/Severing Proteins
43
Q

def: bind at regular intervals along a microtubule wall, allowing for interaction with other cellular structures and filaments

A

Microtubule-Stabiliziing/Bundling proteins

44
Q

def: MAP that causes MTs to form tight bundles in axons

A

Tau

45
Q

def: MAP that promotes the formation of looser bundles in dendrites

A

MAP2

46
Q

what part of the MAP controls the spacing of MTs in the bundle?

A

the extended arm

47
Q

can MTs stay intact for long periods of time?

A

no, they are too unstable, and will de-polymerize unless they are stabilized in some way

48
Q

what can stabilize MTs?

A

+-TIPs capture the growing plus end and protect it form catastrophic subunit loss

49
Q

def: bind to tubulin heterodimers and prevent their polymerization

A

Stathmin/Op18

50
Q

def: act as the ends of microtubules, promoting the peeling of subunits from the ends

A

catastrophins

51
Q

def: proteins that sever MTs

A

katanins

MBB 231 (19 decks)

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